Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$235.57	3.801%	$244.524	$244.52	$244.50	$244.50
Purchase #2	$100.83	8.642%	$109.5437	$109.54	$109.55	$109.50
Purchase #3	$28.29	13.705%	$32.1671	$32.17	$32.15	$32.20
Purchase #4	$129.44	6.299%	$137.5934	$137.59	$137.60	$137.60
Purchase #5	$102.73	12.506%	$115.5774	$115.58	$115.60	$115.60
Purchase #6	$175.63	6.808%	$187.5869	$187.59	$187.60	$187.60
Purchase #7	$216.43	6.497%	$230.4915	$230.49	$230.50	$230.50
7 purchase totals =	$988.92		$1,057.4840	$1,057.48	$1,057.50	$1,057.50